1. Field of the Invention
The present invention relates to a portable electronic device and its adapter. More particularly, the present invention relates to an adapter that turns on or turns off automatically according to connection and disconnection between the adapter and the system end of the portable electronic device.
2. Description of the Related Art
Portable electronic devices, such as personal digital assistants (PDAs) and notebook computers, as very popular due to their mobility, convenience, and versatile functions. Generally, a portable electronic device needs an adapter for providing electric power to the portable electronic device and/or charging the internal battery of the portable electronic device. Such a portable electronic device includes an adapter and a system end. The adapter converts the AC voltage of a wall socket into a DC voltage required by the system end. The system end is the main body of the portable electronic device, which is powered by the DC voltage and performs the versatile functions according to operations of the user.
A conventional adapter is always converting input AC voltage into output DC voltage as long as it is connected to a power source, such as a wall socket, even when it is disconnected from a corresponding system end. This AC/DC conversion consumes electric energy. The electric power consumed by an adapter when it is disconnected from its corresponding system end is called standby power consumption. Conventional adapters waste energy and generate unwanted heat because of their standby power consumption.
The U.S. Pat. No. 6,195,271 discloses an adapter that can reduce its standby power consumption when it is not providing electric power to the system end. This adapter includes two transformers. The first transformer provides the power to drive the system end. When the system end is shut down and does not need input power, the first transformer is turned off and the second transformer provides electric power to a part of the adapter to maintain on/off control of the power source. The adapter reduces its standby power consumption by turning off the first transformer. However, the adapter still consumes electric energy because the second transformer is still working.